The present invention relates to pump jacks for traveling up and down a pole in general, and more particularly to safety means preventing accidental sliding of the pump jack down the pole even when lubricity is being applied.
As has been known, pump jacks of the type under consideration have been employed in scaffolding systems for raising and lowering scaffolding platforms. Typically, a number of pump jack poles are secured in spaced relationship to a house or building to be worked on, and pump jacks are utilized to ride up and down the poles. Scaffolding staging or platforms are extended across the support arms provided on the pump jacks. The workers can stand on the scaffolding staging and operate the pump jacks to move the staging up and down along the pump jack poles.
Each pump jack in such constructions includes a frame with an upper and a lower shackle. A pump arm is pivotally connected to the frame to operate two shackles alternatively. The operation causes the upper shackle to grip the pole permitting the frame to step upward along the pole. The weight thereafter shifts so that the lower shackle grips the pole and the upper shackle steps up to a next position on the pole. In this manner, one of the shackles steps up the pole while the other shackle grips the pole.
The upper shackle can include a forward helical rod which applies a coupling force to the pole to grip the pole. A crank handle coupled to the helical rod permits winding and unwinding of the rod. To lower the pump jack, a release lever releases the lower shackle from engagement with the pole. The crank handle is then operated to unwind the helical rod thereby rolling the pump jack down the pole. In order to prevent accidental unwinding of the crank handle, the handle has a safety locking position in which it is bent inwardly so that it is retained in place by the pump jack frame which blocks the handle to prevent accidental unwinding of the helical rod. A pump jack of the aforedescribed construction has been disclosed, for example, in applicant's Patent No. 4,463,828. A further improvement on such helical rod includes the presence of a safety cover over the helical rod. Such is described in applicant's Patent No. 4,597,471.
One of the most critical concerns when using pump jacks is the safety of the workers standing on the staging supported by the pump jacks. Despite the presence of the handles which should be bent inwardly to prevent accidental unwinding, sometimes workers forget to fold the handle into the safety position. This might cause an accidental slipping of the pump jack down once the weight is placed on the staging.
Pump-jack failures, and subsequent physical harm or even fatal accidents have been also experienced because oil could not be used on handle crank shafts. Without lubricity, however, the handle crank shaft or arm, due to abrasion, grinds down to the point where it can break out from the holder. Non-lubricated shoulder bushings have been used in connections between the crank arm or shaft and the coupling arm of the handle, to minimize wear on the crank shaft. However, lubricity of the crank shaft is still not possible since this would cause unwinding of the crank shaft and spin-out of the roller whereby the pump jack would slide down the pole. Therefore without the lubricity, the possibility of breakage of the crank shaft is still a potential problem.
It has also been found that as the upper shackle is stepping up the pole, there is a tendency for the crank spiral to turn up to about 170.degree. with each upward pumping stroke. This substantially reduces the amount of vertical distance stepped upwardly with each pumping stroke.
Accordingly, there has been need to provide a helical rod of the upper shackle of the pump jack with reliable safety means which would prevent accidental unwinding of the rod and spin-out of the handle even if the worker forgets to place it to the locking position of engagement with the pole, and at the same time permit lubricity of the helical rod crank shaft while at the same time increasing the step-up efficiency.